Microwave performance of AlGaN/AlN/GaN-based single and coupled channels HFETs

R. A. Ferreyra; X. Li; F. Zhang; C. Zhu; N. Izyumskaya; C. Kayis; V. Avrutin; Ü. Özgür; H. Morkoç

doi:10.1117/12.2005165

27 March 2013 Microwave performance of AlGaN/AlN/GaN-based single and coupled channels HFETs

R. A. Ferreyra, X. Li, F. Zhang, C. Zhu, N. Izyumskaya, C. Kayis, V. Avrutin, Ü. Özgür, H. Morkoç

Proceedings Volume 8625, Gallium Nitride Materials and Devices VIII; 86252B (2013) https://doi.org/10.1117/12.2005165
Event: SPIE OPTO, 2013, San Francisco, California, United States

Abstract

In this work we compare electronic transport performance in HFETs based on single channel (SC) GaN/Al_0.30GaN/AlN/GaN (2nm/20nm/1nm/3.5μm) and coupled channel (CC) GaN/Al_0.285GaN/AlN/GaN/AlN/GaN (2nm/20nm/1nm/4nm/1nm/3.5μm) structures. The two structures have similar current gain cut-off frequencies (11.6 GHz for SC and 14 GHz for CC for ~ 1μm gate length) however, the maximum drain current, I_Dmax, is nearly doubled in the CC HFET (0.64 A/mm compared to 0.36 A/mm in SC). HFETs exhibit maximum transconductance (Gm_max) at a bias point close to where maximum f _T occurs: V_GS =-2.25 V and V_DS =12 V and V_GS = -2 V and VDS= 15 V for SC and CC HFETs, respectively. Since threshold voltage (V_th) is ~ -3.75 V for both SC and CC structures, devices are able to work at high frequencies with a high g_m delivering higher ID. This is in contrast with device performance reported by others where f _T is attained at V_GS closer to V_th and therefore with lower ID/I_Dmax ratios and low Gm. Results are consistent in that CC HFET delivers higher I_Dmax because of the higher electron mobility (μ) and higher carrier density (n) in the channel. As the saturation drain current, I_Dsat, is attained at electric fields (~40KV/cm) lower than the critical electric field, E_cr , (~ 150KV/cm for GaN ) the higher f _T in CC HFETs can be attributed, mainly, to a higher μ, which is in agreement with the Hall measurements. A higher μ in CC HFET is attributed to a shorter hot phonon lifetime.

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R. A. Ferreyra, X. Li, F. Zhang, C. Zhu, N. Izyumskaya, C. Kayis, V. Avrutin, Ü. Özgür, and H. Morkoç "Microwave performance of AlGaN/AlN/GaN-based single and coupled channels HFETs", Proc. SPIE 8625, Gallium Nitride Materials and Devices VIII, 86252B (27 March 2013); https://doi.org/10.1117/12.2005165

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